The role of ice blocks in the creation of distinctive proglacial landscapes during and
following glacier outburst floods (jökulhlaups)
In recent years, it has been recognised that ice blocks form a major component of
jökulhlaups. There are, however, very few published hypotheses of ice-block impact
during and following jökulhlaups. The November 1996 jökulhlaup in southern Iceland,
which transported ice blocks as large as 55 metres in diameter on to Skeioarärsandur,
provided an opportunity to study ice-block impact produced during a high-magnitude
flood. This thesis aims to (i) determine the impact of ice blocks on the morphology and
sedimentology of proglacial river channels during and following a jökuihlaup, and (ii)
provide a model which links distinctive landscapes created by ice blocks with specific
controls on ice-block impact.
A range of ice-block related features are produced during and following a jökulhlaup
reflecting glacial and topographical constraints, ice-block characteristics and jökulhlaup
hydraulics. In locations where sediment flux remains high throughout a flood, large ice
blocks form kettle-scours. Rapid sediment deposition around ice blocks results in the
formation and preservation of antidune stoss sides, entirely aggradational ice block
obstacle shadows and hummocky topography. The grounding of ice blocks in flows of low
sediment concentration or total exhumation of buried ice blocks results in the formation of
classic U-shaped obstacle marks. Where channel geometry abruptly expands ice-block
berms form. On outwash fans kettle holes and obstacle marks occur in distinct clusters.
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Kettle holes form post-flood by the in situ melt of (1) progressively buried ice blocks and
(2) small ice blocks incorporated into flow deposits. Ice block debris is superimposed onto
obstacle marks and kettle holes and deposited on the post-flood streambed to form rimmed
kettle holes and obstacle marks and ice-block till mounds respectively. Knowledge of
associations between ice blocks and the bedforms and facies produced during and
following a jökulhlaup will aid jökulhlaup identification and reconstruction in modern and
ancient proglacial environments.